At present, white LED production technology on the market is mainly divided into two major mainstreams:
The first is to use the phosphor to convert the blue or ultraviolet light generated by the blue LED or the ultraviolet UV-LED into two-dipole or three-color white light. This component technology is called a phosphor-converted white LED ( Phosphor Converted-LED);
The second type is a multi-chip white LED, which combines two (or more) LEDs of different color lights to form white light. Currently, white LED products are most commonly used in the market, and blue LED chips are most commonly used in automobiles. In the fields of lighting and mobile phone panels, with the current market analysis of white LED products , phosphor-converted white LEDs can be described as mainstream. (Red and green phosphors are mostly sulfide systems, and such phosphors have poor light-emitting stability and large light decay.)
The following figure summarizes and compares the principles and advantages and disadvantages of various white LEDs. Among them, (a) is the best in structure and color rendering, but the cost is the highest and has not been popularized. The construction method (b) has technology. The most mature and low-cost advantage, but the color shift, color rendering is not good, must be improved with appropriate red and yellow phosphors, in addition, the most serious is the Japanese patent restrictions are difficult to circumvent; and the construction method (c) The white LEDs produced by (d) both have good color rendering, small color, low cost and less serious patent limitations, so the future has great potential for development.
The principle and advantages and disadvantages of using white light to generate white light
How is the phosphor applied to the LED light?
MRKramas et al. found that if the phosphor is randomly placed on the LED chip, the uniformity of illumination is poor as shown in the following figure (a), so the change pattern is as shown in (b), and the phosphor is uniformly applied to the surface of the LED. Figure (c) compares the CCT and Ra values ​​of the two, and finds that the CCT value of the method using the method of (b) is very small.
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